Amount of deferred policy acquisition costs charged to expense in the period, generally in proportion to related revenue earned, estimated gross profits, or over the customer relationship or some other period.

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+ Details

Nature of Operations and Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 item	Sep. 30, 2011	Sep. 30, 2012 item	Sep. 30, 2011	Jan. 02, 2012
Basis of presentation
Participation percentage in quota share reinsurance agreements			100.00%
Number of aggregated major underwriting units of segment	3		3
Deferred acquisition costs that are no longer deferrable					$ 5.6
Amortization expense	$ 0.9	$ 1.4	$ 5.3	$ 5.7
White Mountains Insurance Group Ltd
Basis of presentation
Ownership interest (as a percent)	75.20%		75.20%